ASP.NET MVC: null reference exception using HtmlHelper.TextBox and custom model binder
- by mr.nicksta
I have written a class which implements IModelBinder (see below). This class handles a form which has 3 inputs each representing parts of a date value (day, month, year). I have also written a corresponding HtmlHelper extension method to print out three fields on the form.
When the day, month, year inputs are given values which can be parsed, but a seperate value fails validation, all is fine - the fields are repopulated and the page served to the user as expected.
however when an invalid values are supplied and a DateTime cannot be parsed, i return an arbitrary DateTime so that the fields will be repopulated when returned to the user.
I read up on similar problems people have had and they all seemed to be due to lack of calling SetModelValue(). I wasn't doing this, but even after adding the problem has not been resolved.
public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
{
string modelName = bindingContext.ModelName;
string monthKey = modelName + ".Month";
string dayKey = modelName + ".Day";
string yearKey = modelName + ".Year";
//get values submitted on form
string year = bindingContext.ValueProvider[yearKey].AttemptedValue;
string month = bindingContext.ValueProvider[monthKey].AttemptedValue;
string day = bindingContext.ValueProvider[dayKey].AttemptedValue;
DateTime parsedDate;
if (DateTime.TryParse(string.Format(DateFormat, year, month, day), out parsedDate))
return parsedDate;
//could not parse date time report error, return current date
bindingContext.ModelState.AddModelError(yearKey, ValidationErrorMessages.DateInvalid);
//added this after reading similar problems, does not fix!
bindingContext.ModelState.SetModelValue(modelName, bindingContext.ValueProvider[modelName]);
return DateTime.Today;
}
the null reference exception is thrown when i attempt to create a textbox for the Year property of the date, but strangely not for Day or Month! Can anyone offer an explanation as to why this is?
Thanks :-)
